Field-effect controlled transistor devices with an insulated gate electrode such as MOSFETs or IGBTs are widely used as electronic switches in automotive, industrial, household or consumer electronic applications. These transistor devices are available with voltage blocking capabilities of between several volts and several 100 volts, up to several kilovolts. A field-effect controlled transistor device with an insulated gate electrode includes a source region of a first doping type (conductivity type) in a body region of a second doping type complementary to the first doping type. A drift region of the first conductivity type adjoins the body region and is located between the body region and a drain region. The gate electrode is adjacent the body region, dielectrically insulated from the body region by a gate dielectric, and serves to control a conducting channel in the body region between the source region and the drift region. This type of transistor device is commonly referred to as MOS (Metal Oxide Semiconductor) transistor device although the gate electrode not necessarily includes a metal and the gate dielectric not necessarily includes an oxide.
In an MOS transistor device, the source region, the body region and the drift region form a parasitic (intrinsic) bipolar transistor, with the body region forming the base region of this bipolar transistor. This parasitic bipolar transistor may switch on under overload conditions. Examples of these overload conditions include an avalanche breakdown, cosmic radiation, overcurrent (a short circuit in a load connected in series with the MOS transistor), and commutation of a load connected to the MOS transistor. Switching on the parasitic bipolar transistor causes the MOS transistor to switch on, so that the MOS transistor switches on unintentionally and cannot be controlled by the gate electrode any more. Such switching on of the parasitic bipolar transistor is commonly referred to as latch-up and may lead to an irreversible destruction of the device, if the load (drain-source) current is not limited externally. Even if source and body regions of the MOS transistor are shorted by a metallization, a voltage drop in the body region, that is, between the base and the emitter of the bipolar transistor may occur and turn on the parasitic bipolar transistor.
There is therefore a need to produce a robust transistor device that is not prone to latch-up.